"Thomas Jefferson, that owner of many slaves, chose to begin ..." — David Graeber quote meaning

Thomas Jefferson, that owner of many slaves, chose to begin the Declaration of Independence by directly contradicting the moral basis of slavery, writing "we hold these truths to be self-evident, that all men are created equal, and that they are endowed by their Creator with certain inalienable Rights ..." thus undercutting simultaneously any argument that Africans were racially inferior, and also that they or their ancestors could ever have been justly and legally deprived of their freedom. In doing so, however, he did not propose some radically new conception of rights and liberties. Neither have subsequent political philosophers. For the most part, we've just kept the old ones, but with the word "not" inserted here and there. Most of our most precious rights and freedoms are a series of exceptions to an overall moral and legal framework that suggests we shouldn't really have them in the first place.